A known piston for an internal combustion engine is disclosed in JP2008-297928A (hereinafter referred to as Patent reference 1). According to Patent reference 1, the piston of the internal combustion engine includes a skirt portion being provided at a piston main body, the skirt portion having plural streaks (stripe-shaped grooves) on a surface of the skirt portion formed by a cutting process using a cutting instrument, or by a form rolling process using a roller. According to the piston of the internal combustion engine, the plural streaks extend in parallel to each other in a sliding direction of the piston main body in a state where the plural streaks are inclined in only one direction by a predetermined angle.
However, according to the piston of the internal combustion engine disclosed in Patent reference 1, because the plural streaks are inclined and extend in the only one direction with respect to the sliding direction of the piston main body, a lubricant oil (oil) being positioned in the grooves is considered to be easily discharged from an edge of the groove by moving within the groove in accordance with a reciprocating motion of the piston. Thus, because the oil retaining performance at a sliding portion cannot be sufficiently ensured, the seizure resistance of the piston main body cannot be secured.
A need thus exists for a piston for an internal combustion engine and a manufacturing method thereof which is not susceptible to the drawback mentioned above.